Electromechanical wheel brake device

ABSTRACT

The invention relates to an electromechanical wheel brake device ( 10 ), with an electric motor ( 18 ) that can press a frictional brake lining ( 14 ) against a brake body ( 16 ) (brake disk) by means of a reduction gear ( 34 ) (planetary gear) and a rotation/translation conversion gear ( 48 ) (ball screw). The invention proposes embodying the electric motor ( 18 ) as a transverse flux motor ( 18 ) with three phase windings ( 21 ); each phase winding ( 21 ) has a circular, annular excitation winding ( 22 ) that is disposed inside U-shaped yokes ( 24 ), which are distributed over the circumference of the excitation winding ( 22 ). This embodiment of the electric motor ( 18 ) permits a compact design of the electric motor ( 18 ) in an annular, hollow shaft design so that the reduction gear ( 34 ) and the rotation/translation conversion gear ( 48 ) can be disposed at least partially inside the electric motor ( 18 ).

PRIOR ART

[0001] The invention relates to an electromechanical wheel brake devicewith the features of the preamble to claim 1.

[0002] A wheel brake device of this kind has been disclosed by WO96/03301. The known wheel brake device has an electric motor with anannular rotor, which can rotatingly drive a nut of arotation/translation conversion gear embodied as a helical gear. Therotation/translation conversion gear converts the rotatory drive motionof the electric motor into a translatory motion so that a frictionalbrake lining of the wheel brake device can be pressed against a rotatingbrake body in order to generate a braking force or a braking moment. Inorder to release the wheel brake device, the frictional brake lining canbe lifted up from the brake body by rotating the electric motor in theopposite direction. The known wheel brake device is embodied as a diskbrake, the brake body is a brake disk non-rotatably connected to avehicle wheel. In principle, the wheel brake device can also be used forother kinds of brake such as a drum brake.

ADVANTAGES OF THE INVENTION

[0003] In the wheel brake device according to the invention, with thefeatures of claim 1, the electric motor is embodied as a so-calledtransverse flux motor with an annular rotor. In contrast to conventionalelectric motors, which have a separate excitation coil for each pole,the transverse flux motor according to the invention has only oneexcitation winding per phase winding. The excitation winding is annularand encompasses an imaginary motor axis. In order to produce magneticpoles, the stator has yokes, which are distributed over thecircumference of the excitation winding and can be magnetized bysupplying current to the excitation winding. The yokes are preferablydistributed equidistantly over the circumference, but this is notabsolutely necessary. The supply of current to the excitation windingproduces magnetic fields in the yokes. The annular excitation windingwith the yokes distributed over its circumference will be referred tobelow as the excitation device of the transverse flux motor according tothe invention. The excitation device preferably constitutes a stator ofthe transverse flux motor since this makes it easier to supply current.

[0004] In addition, the transverse flux motor of the wheel brake deviceaccording to the invention has a number of poles, which preferablycorresponds to the number of yokes. The poles can be moved together inrelation to the excitation device, on a circular path in thecircumference direction of the yokes. If the excitation deviceconstitutes the stator of the transverse flux motor, then the polesconstitute its rotor, i.e. they are supported so that they can rotatetogether on a circular path around the imaginary motor axis. In order toproduce a rotary motion, current is supplied to the excitation winding,i.e. the yokes are magnetized and magnetically attract the poles. Thepoles are pulled toward the yokes until the poles and yokes are alignedwith one another. In order to produce the rotating motion, theexcitation winding is supplied with current when the poles are offset inthe circumference direction from the yokes. The poles move toward theyokes, i.e. the rotor rotates, until the poles and yokes are alignedwith one another. Then the supply of current to the excitation windingis interrupted. In order to produce a more uniform concentric running ofthe transverse flux motor and a torque in every rotation position of therotor, the transverse flux motor is preferably provided with three ormore phase windings; each phase winding has an excitation device andassociated poles (claim 3). This also assures that the transverse fluxmotor can start in every rotation position of its rotor and can start inthe desired rotation direction. The supply of current to the excitationwindings of the transverse flux motor of the electromechanical wheelbrake device according to the invention is controlled electronically. Inan embodiment of the transverse flux motor with permanent magnets, twophase windings are sufficient (claim 4). Such an embodiment of theinvention has the advantage of a higher power density.

[0005] The wheel brake device according to the invention has theadvantage that its electric motor requires only one excitation windingper phase winding instead of the usual one coil per pole required inconventional electric motors. Since the winding of coils and theirattachment to the poles and yokes is expensive, this reduces the effortand cost involved in manufacturing. Another advantage of the wheel brakedevice according to the invention is that permanent magnets for itstransverse flux motor can be eliminated, which can further reduce theeffort and cost involved in manufacturing. Another advantage of thetransverse flux motor is increased motor dynamics since it can easily bemanufactured with a large number of poles, depending on how it isdesigned. An increase in the number of poles does not change the numberof windings/coils. An increase in the number of poles therefore does notincrease the manufacturing costs or only increases them slightly; theproblem of not being able to accommodate or mount a large number ofcoils does not occur. Other advantages include an improvement in theefficiency, a volume reduction, and an increase in the power density. Inaddition, depending on how it is designed, the transverse flux motor issuitable for an annular design, as a result of which therotation/translation conversion gear and a reduction gear possiblyconnected between the electric motor and the rotation/translationconversion gear can be accommodated in a cavity inside the annulartransverse flux motor. In addition, situating the electric motor in anannular fashion around the gear produces a large lever arm and thereforea high driving torque of the electric motor.

[0006] Advantageous embodiments and modifications of the inventiondisclosed in claim 1 are the subject of the dependent claims.

DRAWINGS

[0007] The invention will be explained in detail below in conjunctionwith exemplary embodiments shown in the drawings.

[0008]FIG. 1 shows an axial section through an electromechanical wheelbrake device according to the invention, with a transverse flux motor inan external rotor design;

[0009]FIG. 2 schematically depicts a rotor/stator device of thetransverse flux motor from FIG. 1;

[0010]FIG. 3 shows a modified embodiment of the invention, with aninternal rotor transverse flux motor;

[0011]FIG. 4 shows another modified embodiment of the invention, with adisk armature transverse flux motor;

[0012]FIG. 5 schematically depicts a rotor/stator device of thetransverse flux motor from FIG. 4; and

[0013]FIG. 6 shows another embodiment of the invention, with a diskarmature transverse flux motor.

DESCRIPTION OF THE FIRST EXEMPLARY EMBODIMENT

[0014] The electromechanical wheel brake device 10 according to theinvention shown in FIG. 1 is embodied as a disk brake device. It has acaliper 12 in which two frictional brake linings 14 are mounted, betweenwhich a brake disk 16 is supported so that it can rotate and isnon-rotatably connected to a vehicle wheel, not shown. In order togenerate a braking force or a braking moment, the frictional brakelining 14 shown on the right in the drawing is pressed against one sideof the brake disk 16. A reaction force of the compressive force of theone frictional brake lining 14 shifts the caliper 12, which is embodiedas a floating caliper, to one side in an intrinsically known fashion(toward the right in the drawing), so that the other frictional brakelining 14 is also pressed against the other side of the brake disk 16and therefore a braking force is exerted on the brake disk 16 by the twofrictional brake linings 14.

[0015] The wheel brake device 10 has an electric motor 18 to actuate it,which is embodied according to the invention as a transverse flux motor18 and in the exemplary embodiment shown in FIG. 1, is embodied as aso-called external rotor motor. The electric motor 18 is annular indesign, which can also be referred to as a hollow shaft design. A rotor20 of the electric motor 18 is embodied as tubular or cup-shaped. Theelectric motor 18 of the wheel brake device 10, which is embodied as atransverse flux motor 18, has three phase windings, which are disposednext to one another in the axial direction, encompassing a brake caliperhousing. The design and function of the transverse flux motor 18 will beexplained below in conjunction with FIG. 2, which schematically depictsa phase winding of the transverse flux motor 18. Each phase winding ofthe transverse flux motor 18 has a circular excitation coil 22, whichcoaxially encompasses an imaginary motor axis of the transverse fluxmotor. The excitation winding 22 is inserted into U-shaped yokes 24,which are distributed equidistantly over the circumference of theexcitation winding 22. For example, the transverse flux motor 18 has 12yokes 24. The U-shaped yokes 24 are open toward the outside in theexternal rotor motor shown in FIG. 1. The yokes 24 and the excitationwinding 22 disposed inside the yokes 24 constitute an excitation device22, 24 of the transverse flux motor 18, which in the exemplaryembodiment shown, simultaneously constitutes a stator of the transverseflux motor 18.

[0016] The rotor 20 of the transverse flux motor 18 is embodied ascup-shaped; it has a circumference wall 26, which is of one piece withan end wall 28. An inside surface of the circumference wall 26 of therotor 20 is provided with a kind of denticulation that constitutesinward protruding poles 30. The rotor 26 has the same number of poles 30as the stator 22, 24 has yokes 24; the poles 30 are spaced apart fromeach other by the same angular interval in the circumference directionas the yokes 24.

[0017] If the yokes 30 of the rotor 26 are disposed in a position thatis offset from the yokes 24 of the stator 22, 24, as shown in FIG. 2,then when the excitation winding disposed inside the yokes 24 issupplied with current, then they are pulled by magnetic force toward theyokes 24, which exerts a torque on the rotor 20 of the transverse fluxmotor 18 and sets it into rotation. The torque is exerted on the rotor20 until the poles 30 and the yokes 24 are congruently aligned with oneanother. In this rotation position of the rotor 20, the supply ofcurrent 20 to the excitation winding 22 of this phase winding of thetransverse flux motor 18 is and the excitation winding 22 of the nextphase winding is supplied with current. The next phase winding is theone in which the angular offset between the poles 30 and the yokes 24 issmaller in the rotation direction of the rotor 26. As a result, therotor 26 is rotated further until the poles 30 and the yokes 24 of thenext phase winding are congruently aligned with one another, whereuponthe supply of current to the excitation winding 22 of this phase windingis also switched off and the excitation winding 22 of the third phasewinding is supplied with current. A continuous, successive supply ofcurrent to the excitation windings 22 of the three phase windings of thetransverse flux motor 18 sets its rotor into rotation and keeps itrotating. In order to turn the transverse flux motor 18 in the oppositedirection, the sequence of the supply of current to the excitationwindings 22 is reversed. Since in one phase winding of the transverseflux motor 18, the poles 30 have an angular offset in relation to theyokes 24 in one circumference direction and the poles 30 of anotherphase winding have an offset in relation to the yokes 24 of this otherphase winding in the opposite circumference direction, the transverseflux motor 18 can start in every rotation position of its rotor 20 andcan start in the desired rotation direction.

[0018] Either the poles 30 or the yokes 24 of the three phase windingsof the transverse flux motor 18 are offset from one another in thecircumference direction, preferably by ⅓ of their spacing in thecircumference direction, i.e. the three phase windings of the transverseflux motor 18 have a phase offset of ⅓ the angular interval of theirpoles 30 and yokes 24 from one another in the circumference direction.

[0019] The supply of current to the excitation windings 22 is controlledelectronically as a function of the angular position of the rotor 26 inrelation to the stator 22, 24. A for the control of the supply ofcurrent to the excitation windings 22 is performed by means of a radialsensor bearing 32, which supports the rotor 20 of the transverse fluxmotor 18 so that it can rotate in the caliper 12. Sensor bearings 32 ofthis kind are intrinsically known and therefore need not be explained indetail since they are not the actual subject of the invention.

[0020] The three phase windings of the transverse flux motor 18 aredisposed next to one another in the axial direction on a housing of thebrake caliper 12. The excitation winding 22 and yokes 24 that constitutethe stator are permanently affixed to an outside of the housing of thebrake caliper 12 and are enclosed by the circumference wall 26 of therotor 20, separated from it by an air gap.

[0021] The wheel brake device 10 according to the invention has areduction gear 34, which is accommodated inside a cavity of theannularly embodied transverse flux motor 18. The reduction gear 34 inthe exemplary embodiment of the invention shown is embodied as atwo-stage planetary gear 34. A first stage of the planetary gear 34 hasa sun wheel 36, which is non-rotatably connected to the end wall 28 ofthe rotor 20 and meshes with three planet wheels 38, which in turn meshwith an internal gearing 40 that is provided on the inside of acylindrical cavity in the brake caliper 12. The internal gearing 40constitutes a fixed ring gear 40 of the planetary gear 34.

[0022] The planet carrier 42 of the first stage of the planetary gear 34is non-rotatably connected to a sun wheel 44 of the second stage of theplanetary gear 34 and this sun wheel 44 meshes with planet wheels 46 ofthe second stage of the planetary gear 34. The planet wheels 46 of thesecond stage of the planetary gear 34 mesh with the internal gearing 40of the brake caliper 12, which also constitutes a fixed ring gear of thesecond stage of the planetary gear 34.

[0023] In order to convert the rotational motion of the transverse fluxmotor 18, which is reduced by the planetary gear 34, into atranslational motion for pressing the fractional brake linings 14against the brake disk 16, the wheel brake device 10 according to theinvention has a helical gear 48, which in the exemplary embodiment ofthe invention that is depicted and described here, is embodied as a ballscrew 48. The rotation/translation conversion gear 48 is disposedpartially inside the cavity of the annularly embodied transverse fluxmotor 18, which by and large results in a compact design of the wheelbrake device 10. The rotation/translation conversion gear 48, which isembodied as a ball screw 48, has a spindle 50, which is supported with aradial needle bearing 52 so that it can rotate in the brake caliper 12and is supported axially in relation to the brake caliper 12 by means ofan axial ball bearing 54. A serrated connection 56 serves to connect thespindle 50 in a non-rotating fashion to a planet carrier 58 of thesecond stage of the planetary gear 34. The spindle 50 of the ball screw48 engages by means of balls 60 with a nut 62 of the ball screw 48. Oneof the two frictional brake linings 14 is disposed on an end of the nut62 oriented away from the planetary gear 34. By means of the planetarygear 34, the transverse flux motor 18 can drive the spindle 54 of theball screw to rotate and the nut 62 of the ball screw 48 moves so thatthe frictional brake linings 14 can be pressed against the brake disk16. The frictional brake linings 14 can be lifted up again from thebrake disk 16 by rotating the transverse flux motor 18 in the oppositedirection.

DESCRIPTION OF THE SECOND EXEMPLARY EMBODIMENT

[0024] In order to avoid repetition, only to differences between theelectromechanical wheel brake device 10 according to the invention shownin FIG. 3 and the wheel brake device 10 shown in FIG. 1 will beexplained. Otherwise, please refer to the explanations made inconjunction with FIG. 1. Parts, which are the same, are provided withthe same reference numerals. In the wheel brake device 10 shown in FIG.3, the transverse flux motor 18 is embodied differently than in FIG. 1.The transverse flux motor 18 in FIG. 3 is likewise embodied as a hollowshaft motor, but is designed as a so-called internal rotor motor. In thetransverse flux motor 18 shown in FIG. 3, the excitation device 22, 24with the excitation winding 22 and the U-shaped yokes 24 is disposedoutside the likewise cup-shaped rotor 20. The U-shaped yokes 24 aretherefore placed onto the excitation winding 22 from the outside, theopening of the yokes 24 points radially inward toward the cylindricalcircumference wall 22 of the rotor 20. The denticulation of the rotor 20that constitutes the poles 30 is disposed on the outside of thecircumference wall 26. With the exception of the excitation device 22,24, which is disposed on an outside of the cup-shaped rotor 20 andsimultaneously constitutes the stator of the transverse flux motor 18,and a therefore smaller diameter of the rotor 20, the transverse fluxmotor 18 from FIG. 3 has the same design and functions in the samemanner as the transverse flux motor 18 that is shown in FIG. 1 andexplained above. The remaining design of the wheel brake device 10 fromFIG. 3, with the two-stage planetary gear 34 and therotation/translation conversion gear 48 embodied as a ball screw 48,corresponds to that of the one in FIG. 1 and functions in the same way.

DESCRIPTION OF THE THIRD AND FOURTH EXEMPLARY EMBODIMENT OF THEINVENTION

[0025] In the embodiment of the invention shown in FIG. 4, the wheelbrake device 10 has a transverse flux motor 18 of the disk armaturetype. The design of the transverse flux motor 18 will be explained inconjunction with the depiction in FIG. 5. Here, too, each phase winding21 of the transverse flux motor 18 has a circular excitation winding 22,which concentrically encompasses an imaginary motor axis. By contrast toFIGS. 1 and 3, the U-shaped yokes 24 are installed onto the excitationwinding 22 laterally, i.e. with axially parallel legs 63. The rotor 20has a pole ring 64, which is provided with a denticulation on theoutside and inside that constitutes the poles 30. The poles 30 thereforeprotrude radially outward and inward from the pole ring 64. The polering 64 is disposed next to the excitation winding 22 in the axialdirection, inside an opening of the U-shaped yokes 24 that are opentoward the side. As described above in relation to FIG. 2, by supplyingcurrent to the excitation winding 22, the poles 30 are moved in thecircumferential direction by magnetic force until they are alignedcongruently with the yokes 24 so that repeated, successive supplying ofcurrent to the excitation windings 22 of the three phase windings 21 ofthe transverse flux motor 18 can set its rotor 20 into rotation. Thepole ring 64 is attached to an annular disk 66, which is disposed in aradial plane and is non-rotatably affixed to an outside of thecylindrical circumference wall 26 of the rotor 20. The annular disk 66is not shown in FIG. 5 because it would completely cover the excitationwinding 22 and the pole ring 64 and would partially cover the yokes 24,which would make it impossible to see these parts.

[0026] With the exception of the above-explained design of thetransverse flux motor 18, the wheel brake device 10 shown in FIG. 4 hasthe same design and functions in the same manner as the above-describedwheel brake device 10 in FIG. 1. In order to avoid repetition, pleaserefer to the explanations made above in conjunction with FIG. 1.

[0027] With FIG. 6 shows a modified embodiment of wheel brake device 10shown in FIG. 4, with a modified transverse flux motor 18, which islikewise of the disk armature type. In this embodiment of the invention,only two of the three phase windings 21 of the transverse flux motor 18are disposed outside the cup-shaped rotor 20. The excitation windings 22of these two phase windings 21 of the transverse flux motor 18 aredisposed on both sides of the annular disk 66; the open sides of theirU-shaped yokes 24 are oriented toward each other, i.e. pointing towardthe annular disk 66. The annular disk 66 is provided with adenticulation on both sides and these denticulations constitute thepoles 30 of the rotor 20. In order to produce the phase shift describedabove in conjunction with FIGS. 1 and 2, the yokes 30 of the two phasewindings 21 are disposed offset from one another in the circumferencedirection by ⅓ the distance between the yokes 30 of a phase winding 21,which is why in FIG. 6, the yokes 30 on the right side of the annulardisk 66 are shown in a sectional view and the yokes 30 on the left sideof the annular disk 66 are shown in an aspect view.

[0028] The third phase winding 21 of the transverse flux motor 18 of thewheel brake device 10 shown in FIG. 6 is disposed inside one of the twoother phase windings 21 on an outside, i.e. next to the end wall 28 ofthe rotor 20 in the axial direction. The end wall 28 is in turn providedwith a denticulation, which constitutes the poles 30 of this third phasewinding 21 of the transverse flux motor 18. The excitation winding 22 ofthis third phase winding 21 of the transverse flux motor 18 has asmaller diameter than the excitation windings 22 of both of the otherphase windings 21; the excitation winding 22 of the third phase winding21 likewise constitutes a circle, which is disposed concentric to animaginary motor axis of the transverse flux motor 18. The excitationwinding 22 of the third phase winding 21 also has U-shaped yokes 24placed onto it, whose open ends are oriented toward the poles 30 of thethird phase winding 21 of the transverse flux motor 18. The function ofthe transverse flux motor 18 of the embodiment of the wheel brake device10 shown in FIG. 6 is the same as the one shown in FIG. 1. In FIG. 6, amore compact design of the transverse flux motor 18 has been chosen inwhich the excitation device 22, 24 of the third phase winding 21 isdisposed inside the excitation device 22, 24 of one of the two otherphase windings 21.

[0029] The rest of the design of the wheel brake device 10 shown in FIG.6, with the two-stage planetary gear 34 disposed completely inside therotor 20 of the transverse flux motor 18 and with therotation/translation conversion gear 48 embodied as a ball screw 48,corresponds to the design of these parts in the wheel brake device 10shown in FIG. 1.

[0030] In order to produce an auxiliary brake function, the wheel brakedevice 10 shown in FIG. 6 also has an auxiliary brake 68. The auxiliarybrake 68 is embodied as an electromagnetic brake 68, which immobilizesthe spindle 50 of a ball screw 48 when without current and can bereleased when it is supplied with current. The electromagnetic brake 68has an armature plate 70, which is provided with a circular disk-shapedfrictional brake lining 72, with which it is pressed against a housingcover 76 of the brake caliper 12 by a helical compression spring 74. Inthis manner, the armature plate 70 of the electromagnetic brake 68 isimmobilized when without current. A pin 78 protrudes from the armatureplate 70 and by means of a serrated connection 80, engages in anon-rotatable, axially mobile fashion in a sleeve 82, which protrudesfrom the end wall 28 of the rotor 20 and is of one piece with it. Forreleasing, the electromagnetic brake 68 has a coil 84, which is disposedin an annular yoke 86 that has a U-shaped cross section. If the coil 84is supplied with current, then it attracts the armature disk 70 withmagnetic force so that the armature disk 70 is lifted up from thehousing cover 76, counter to the force of the helical compression spring74, and can therefore rotate. Since the electromagnetic brake 68, whenwithout current, holds the rotor 20 and, by means of the planetary gear34, the spindle 50 of the ball screw 48 so that they cannot rotate, oncea braking force of the wheel brake device 10 is produced by thetransverse flux motor 18, this braking force is maintained even withouta supply of current to the transverse flux motor 18, as a result ofwhich the wheel brake device 10 can also be used as an auxiliary brake.The electromagnetic brake 68 can also be immobilized during a brakingprocedure if a braking force of the wheel brake device 10 produced bythe transverse flux motor 18 must be kept constant, which means that thetransverse flux motor 18 does not have to be supplied with current inorder to keep the braking force constant. When the electromagnetic brake68 is released, i.e. supplied with current, the transverse flux motor isonly supplied with current in order to apply and increase the brakingforce and to completely release the wheel brake device 10. The ballscrew 48 is selflocking-free so that a braking force of the wheel brake10 produced by the transverse flux motor 18 automatically decreases to alow residual braking force.

1. An electromechanical wheel brake device, with an electric motor thathas an annular rotor, with a rotation/translation conversion gear thatcan be driven to rotate by the electric motor, and with a frictionalbrake lining that can be pressed against a brake body by means of therotation/translation conversion gear, characterized in that the electricmotor (18) is embodied as a transverse flux motor (18) with an annularexcitation winding (22) that encompasses an imaginary motor axis, inwhich the electric motor (18) has a number of yokes (24), which aredistributed over the circumference of the excitation winding (22) andcan be excited by this winding, and with a number of poles (30) thatpreferably corresponds to the number of yokes (24), which poles (30) areguided so that they can move together in relation to the yokes (34), ona circular path in the circumference direction of the yokes (24) and, inorder to generate a circular motion, can be magnetically attracted bythe yokes (24) through excitation of the yokes (24).
 2. Theelectromechanical wheel brake device according to claim 1, characterizedin that the yokes (24) are embodied as U-shaped and the excitationwinding (22) is disposed inside the yokes (24).
 3. The electromechanicalwheel brake device according to claim 1, characterized in that thetransverse flux motor (18) has three or more phase windings (21)—eachwith an excitation winding (22), a number of yokes (24), and associatedpoles (30).
 4. The electromechanical wheel brake device according toclaim 1, characterized in that the transverse flux motor (18) haspermanent magnets.
 5. The electromechanical wheel brake device accordingto claim 1, characterized in that the wheel brake device (10) has areduction gear (34), which is connected between the electric motor (18)and the rotation/translation conversion gear (48).
 6. Theelectromechanical wheel brake device according to claim 5, characterizedin that the reduction gear (34) is disposed inside the rotor (20) of theelectric motor (18) and the rotation/translation conversion gear (48) isdisposed at least partially inside the rotor (20) of the electric motor(18).
 7. The electromechanical wheel brake device according to claim 1,characterized in that the rotation/translation conversion gear (48) isembodied as a ball screw (48).
 8. The electromechanical wheel brakedevice according to claim 1, characterized in that therotation/translation conversion gear (48) is selflocking-free.
 9. Theelectromechanical wheel brake device according to claim 1, characterizedin that the wheel brake device (10) has an auxiliary brake (68), whichcan immobilize the rotation/translation conversion gear (48).
 10. Theelectromechanical wheel brake device according to claim 1, characterizedin that the rotation/translation conversion gear (48) is embodied as ahelical gear (48) and that a spindle (50) of the helical gear (48) isdriven to rotate.